/*
 * Copyright (C) 2008 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.sharad.quizbowl.ui.client.util.guava;

import java.io.IOException;
import java.util.AbstractList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;

/**
 * An object which joins pieces of text (specified as an array, {@link Iterable}
 * , varargs or even a {@link Map}) with a separator. It either appends the
 * results to an {@link Appendable} or returns them as a {@link String}.
 * Example:
 * 
 * <pre>
 * {@code
 * 
 *   Joiner joiner = Joiner.on("; ").skipNulls();
 *    . . .
 *   return joiner.join("Harry", null, "Ron", "Hermione");}
 * </pre>
 * 
 * This returns the string {@code "Harry; Ron; Hermione"}. Note that all input
 * elements are converted to strings using {@link Object#toString()} before
 * being appended.
 * 
 * <p>
 * If neither {@link #skipNulls()} nor {@link #useForNull(String)} is specified,
 * the joining methods will throw {@link NullPointerException} if any given
 * element is null.
 * 
 * @author Kevin Bourrillion
 * @since 2010.01.04 <b>stable</b> (imported from Google Collections Library)
 */
public class Joiner {
	/**
	 * Ensures that an object reference passed as a parameter to the calling
	 * method is not null.
	 * 
	 * @param reference
	 *            an object reference
	 * @return the non-null reference that was validated
	 * @throws NullPointerException
	 *             if {@code reference} is null
	 */
	public static <T> T checkNotNull(T reference) {
		if (reference == null) {
			throw new NullPointerException();
		}
		return reference;
	}

	/**
	 * Ensures that an object reference passed as a parameter to the calling
	 * method is not null.
	 * 
	 * @param reference
	 *            an object reference
	 * @param errorMessage
	 *            the exception message to use if the check fails; will be
	 *            converted to a string using {@link String#valueOf(Object)}
	 * @return the non-null reference that was validated
	 * @throws NullPointerException
	 *             if {@code reference} is null
	 */
	public static <T> T checkNotNull(T reference, Object errorMessage) {
		if (reference == null) {
			throw new NullPointerException(String.valueOf(errorMessage));
		}
		return reference;
	}

	/**
	 * Returns a joiner which automatically places {@code separator} between
	 * consecutive elements.
	 */
	public static Joiner on(String separator) {
		return new Joiner(separator);
	}

	/**
	 * Returns a joiner which automatically places {@code separator} between
	 * consecutive elements.
	 */
	public static Joiner on(char separator) {
		return new Joiner(String.valueOf(separator));
	}

	private final String separator;

	private Joiner(String separator) {
		this.separator = checkNotNull(separator);
	}

	private Joiner(Joiner prototype) {
		this.separator = prototype.separator;
	}

	/**
	 * Appends the string representation of each of {@code parts}, using the
	 * previously configured separator between each, to {@code appendable}.
	 */
	public <A extends Appendable> A appendTo(A appendable, Iterable<?> parts)
			throws IOException {
		checkNotNull(appendable);
		Iterator<?> iterator = parts.iterator();
		if (iterator.hasNext()) {
			appendable.append(toString(iterator.next()));
			while (iterator.hasNext()) {
				appendable.append(separator);
				appendable.append(toString(iterator.next()));
			}
		}
		return appendable;
	}

	/**
	 * Appends the string representation of each of {@code parts}, using the
	 * previously configured separator between each, to {@code appendable}.
	 */
	public final <A extends Appendable> A appendTo(A appendable, Object[] parts)
			throws IOException {
		return appendTo(appendable, Arrays.asList(parts));
	}

	/**
	 * Appends to {@code appendable} the string representation of each of the
	 * remaining arguments.
	 */
	public final <A extends Appendable> A appendTo(A appendable, Object first,
			Object second, Object... rest) throws IOException {
		return appendTo(appendable, iterable(first, second, rest));
	}

	/**
	 * Appends the string representation of each of {@code parts}, using the
	 * previously configured separator between each, to {@code builder}.
	 * Identical to {@link #appendTo(Appendable, Iterable)}, except that it does
	 * not throw {@link IOException}.
	 */
	public final StringBuilder appendTo(StringBuilder builder, Iterable<?> parts) {
		try {
			appendTo((Appendable) builder, parts);
		} catch (IOException impossible) {
			throw new AssertionError(impossible);
		}
		return builder;
	}

	/**
	 * Appends the string representation of each of {@code parts}, using the
	 * previously configured separator between each, to {@code builder}.
	 * Identical to {@link #appendTo(Appendable, Iterable)}, except that it does
	 * not throw {@link IOException}.
	 */
	public final StringBuilder appendTo(StringBuilder builder, Object[] parts) {
		return appendTo(builder, Arrays.asList(parts));
	}

	/**
	 * Appends to {@code builder} the string representation of each of the
	 * remaining arguments. Identical to
	 * {@link #appendTo(Appendable, Object, Object, Object[])}, except that it
	 * does not throw {@link IOException}.
	 */
	public final StringBuilder appendTo(StringBuilder builder, Object first,
			Object second, Object... rest) {
		return appendTo(builder, iterable(first, second, rest));
	}

	/**
	 * Returns a string containing the string representation of each of
	 * {@code parts}, using the previously configured separator between each.
	 */
	public final String join(Iterable<?> parts) {
		return appendTo(new StringBuilder(), parts).toString();
	}

	/**
	 * Returns a string containing the string representation of each of
	 * {@code parts}, using the previously configured separator between each.
	 */
	public final String join(Object[] parts) {
		return join(Arrays.asList(parts));
	}

	/**
	 * Returns a string containing the string representation of each argument,
	 * using the previously configured separator between each.
	 */
	public final String join(Object first, Object second, Object... rest) {
		return join(iterable(first, second, rest));
	}

	/**
	 * Returns a joiner with the same behavior as this one, except automatically
	 * substituting {@code nullText} for any provided null elements.
	 */
	public Joiner useForNull(final String nullText) {
		checkNotNull(nullText);
		return new Joiner(this) {
			@Override
			CharSequence toString(Object part) {
				return (part == null) ? nullText : Joiner.this.toString(part);
			}

			@Override
			public Joiner useForNull(String nullText) {
				checkNotNull(nullText); // weird, just to satisfy
										// NullPointerTester!
				// TODO: fix that?
				throw new UnsupportedOperationException(
						"already specified useForNull");
			}

			@Override
			public Joiner skipNulls() {
				throw new UnsupportedOperationException(
						"already specified useForNull");
			}
		};
	}

	/**
	 * Returns a joiner with the same behavior as this joiner, except
	 * automatically skipping over any provided null elements.
	 */
	public Joiner skipNulls() {
		return new Joiner(this) {
			@Override
			public <A extends Appendable> A appendTo(A appendable,
					Iterable<?> parts) throws IOException {
				checkNotNull(appendable, "appendable");
				checkNotNull(parts, "parts");
				Iterator<?> iterator = parts.iterator();
				while (iterator.hasNext()) {
					Object part = iterator.next();
					if (part != null) {
						appendable.append(Joiner.this.toString(part));
						break;
					}
				}
				while (iterator.hasNext()) {
					Object part = iterator.next();
					if (part != null) {
						appendable.append(separator);
						appendable.append(Joiner.this.toString(part));
					}
				}
				return appendable;
			}

			@Override
			public Joiner useForNull(String nullText) {
				checkNotNull(nullText); // weird, just to satisfy
										// NullPointerTester!
				throw new UnsupportedOperationException(
						"already specified skipNulls");
			}

			@Override
			public MapJoiner withKeyValueSeparator(String kvs) {
				checkNotNull(kvs); // weird, just to satisfy NullPointerTester!
				throw new UnsupportedOperationException(
						"can't use .skipNulls() with maps");
			}
		};
	}

	/**
	 * Returns a {@code MapJoiner} using the given key-value separator, and the
	 * same configuration as this {@code Joiner} otherwise.
	 */
	public MapJoiner withKeyValueSeparator(String keyValueSeparator) {
		return new MapJoiner(this, checkNotNull(keyValueSeparator));
	}

	/**
	 * An object that joins map entries in the same manner as {@code Joiner}
	 * joins iterables and arrays.
	 */
	public static class MapJoiner {
		private Joiner joiner;
		private String keyValueSeparator;

		private MapJoiner(Joiner joiner, String keyValueSeparator) {
			this.joiner = joiner;
			this.keyValueSeparator = keyValueSeparator;
		}

		/**
		 * Appends the string representation of each entry of {@code map}, using
		 * the previously configured separator and key-value separator, to
		 * {@code appendable}.
		 */
		public <A extends Appendable> A appendTo(A appendable, Map<?, ?> map)
				throws IOException {
			checkNotNull(appendable);
			Iterator<? extends Map.Entry<?, ?>> iterator = map.entrySet()
					.iterator();
			if (iterator.hasNext()) {
				Entry<?, ?> entry = iterator.next();
				appendable.append(joiner.toString(entry.getKey()));
				appendable.append(keyValueSeparator);
				appendable.append(joiner.toString(entry.getValue()));
				while (iterator.hasNext()) {
					appendable.append(joiner.separator);
					Entry<?, ?> e = iterator.next();
					appendable.append(joiner.toString(e.getKey()));
					appendable.append(keyValueSeparator);
					appendable.append(joiner.toString(e.getValue()));
				}
			}
			return appendable;
		}

		/**
		 * Appends the string representation of each entry of {@code map}, using
		 * the previously configured separator and key-value separator, to
		 * {@code builder}. Identical to {@link #appendTo(Appendable, Map)},
		 * except that it does not throw {@link IOException}.
		 */
		public StringBuilder appendTo(StringBuilder builder, Map<?, ?> map) {
			try {
				appendTo((Appendable) builder, map);
			} catch (IOException impossible) {
				throw new AssertionError(impossible);
			}
			return builder;
		}

		/**
		 * Returns a string containing the string representation of each entry
		 * of {@code map}, using the previously configured separator and
		 * key-value separator.
		 */
		public String join(Map<?, ?> map) {
			return appendTo(new StringBuilder(), map).toString();
		}

		/**
		 * Returns a map joiner with the same behavior as this one, except
		 * automatically substituting {@code nullText} for any provided null
		 * keys or values.
		 */
		public MapJoiner useForNull(String nullText) {
			return new MapJoiner(joiner.useForNull(nullText), keyValueSeparator);
		}
	}

	CharSequence toString(Object part) {
		return (part instanceof CharSequence) ? (CharSequence) part : part
				.toString();
	}

	private static Iterable<Object> iterable(final Object first,
			final Object second, final Object[] rest) {
		checkNotNull(rest);
		return new AbstractList<Object>() {
			@Override
			public int size() {
				return rest.length + 2;
			}

			@Override
			public Object get(int index) {
				switch (index) {
				case 0:
					return first;
				case 1:
					return second;
				default:
					return rest[index - 2];
				}
			}
		};
	}
}